The present invention relates to microwave transmitters employing field effect transistors which make it possible to produce wholly transistorised Doppler type radars, even in the power stages of the transmitter. Such Doppler radars are used in particular for terrestrial surveillance, and it is of great importance in this case to reduce weight, bulk and power consumption. The substitution of transistors for vacuum tubes permits a substantial gain in this respect.
It is known that transistors and in particular field effect transistors may be utilised to amplify microwaves, in particular in the so-called I band situated in the region of 10 GHz. These transistors are commonly produced by using gallium arsenide as a semiconductor. These can operate on the class A mode only, giving a substantially constant consumption and a wastage of power during the idle periods consisting of the intervals between the microwave pulses characteristic of radar operation,. The power saving which could be hoped for by utilising such transistors is thus considerably reduced as compared to vacuum tubes which can operate in class C mode and which are consequently supplied only during the transmission pulses.